1. Field of the Invention
The present invention relates to transmission power control of a communication apparatus.
2. Description of the Related Art
Public radio communications and the like have already implemented transmission power control of battery-driven communication apparatuses and prolonged their driving time. Various schemes have been proposed to control transmission power. For example, patent reference 1: U.S. Pat. No. 6,119,018 (Japanese Patent Laid-Open No. 9-326754) describes a technique of causing a host station to transmit an optimum transmission power control signal to a mobile station. The mobile station subordinately controls its transmission power in accordance with the signal.
PTP (Picture Transfer Protocol) is an image transfer protocol by camera control. A side to request PTP session establishment is called an initiator. The other side to respond to the request is called a responder. After PTP session establishment, command-response communication is done so that the initiator requests an operation, and the responder responds to it. The PTP is popularly used in, e.g. digital still cameras (to be referred to as DSCs hereinafter) and printers.
A communication apparatus that subordinately controls its transmission power in accordance with an instruction from a control station, as in the above-described public radio communication, can minimize the transmission power. Even a communication apparatus that executes autonomous transmission power control can reduce the transmission power if the transmission power of the communication partner is fixed.
However, when a pair of communication apparatuses (e.g., DSCs with built-in wireless LAN) autonomously controls their transmission power, the transmission power of each communication apparatus may be too high or too low. This may increase power consumption or disable communication. For example, in wireless LAN based on IEEE802.11b, the temporal length of a maximum data packet transmitted from a transmitting-side communication apparatus is about eight times that of an acknowledge packet transmitted from a receiving-side communication apparatus. Hence, an increase in power consumption of the transmitting-side communication apparatus poses a problem from the viewpoint of power saving.